This invention relates to a process for preparing 1-(4-fluorophenyl)-3(R)-(3(S)-hydroxy-3-(4-fluorophenyl)propyl)-4(S)-(4 -hydroxyphenyl)-2-azetidinone and 1-(4-fluorophenyl)-3(R)-(3(S)-hydroxy-3-phenylpropyl)-4(S)-(4-hydroxypheny l)-2-azetidinone, compounds useful as hypocholesterolemic agents, and to the preparation of 1-(4-fluorophenyl)-3(R)-(3-(4-fluorophenyl)-3-oxopropyl)-4(S)-(4-benzyloxy phenyl)-2-azetidinone and 1-(4-fluorophenyl)-3(R)-(3-phenyl-3-oxopropyl)-4(S)-(4-benzyloxyphenyl)-2- azetidinone, intermediates in that process.
WO 95/08532 discloses a genus of hypocholesterolemic agents comprising the 3-hydroxypropyl-substituted azetidinones named above and describes several processes suitable for preparing said azetidinones. WO 93/02048 discloses stereoselective processes for producing azetidinones comprising cyclizing intermediates which include the 3-position and 4-position substituents desired in the final product. PCT/US94/07291 discloses a modification of the processes disclosed in WO 93/02048 wherein the .beta.-aminoamides are cyclized by reating with a silylating agent and a fluoride ion catalyst. WO95/26334 discloses chiral .beta.-amino esters, a process for preparing them, and a process for cyclizing a chiral .beta.-amino ester to obtain a chiral 3-unsubstituted azetidinone. The PCT publications and application are related, respectively, to U.S. Ser. Nos. 08/257,593 (filed Jun. 9, 1994), 08/178,312 (filed Jan. 11, 1994), 08/089,357 (filed Jul. 9, 1993) and 08/403,081 (filed Mar. 13, 1995), all incorporated herein by reference.